From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Thu, 20 Jul 2017 17:00:02 -0400
Subject: [PATCH] NFS/filelayout: Fix racy setting of fl->dsaddr in
filelayout_check_deviceid()
Git-commit: 1ebf980127924c639e2b85c08468311ba1c95b70
Patch-mainline: v4.13-rc2
References: bsc#1105190
We must set fl->dsaddr once, and once only, even if there are multiple
processes calling filelayout_check_deviceid() for the same layout
segment.
Reported-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Acked-by: NeilBrown <neilb@suse.com>
---
fs/nfs/filelayout/filelayout.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
--- a/fs/nfs/filelayout/filelayout.c
+++ b/fs/nfs/filelayout/filelayout.c
@@ -570,6 +570,10 @@ filelayout_check_deviceid(struct pnfs_la
struct nfs4_file_layout_dsaddr *dsaddr;
int status = -EINVAL;
+ /* Is the deviceid already set? If so, we're good. */
+ if (fl->dsaddr != NULL)
+ return 0;
+
/* find and reference the deviceid */
d = nfs4_find_get_deviceid(NFS_SERVER(lo->plh_inode), &fl->deviceid,
lo->plh_lc_cred, gfp_flags);
@@ -581,8 +585,6 @@ filelayout_check_deviceid(struct pnfs_la
if (filelayout_test_devid_unavailable(&dsaddr->id_node))
goto out_put;
- fl->dsaddr = dsaddr;
-
if (fl->first_stripe_index >= dsaddr->stripe_count) {
dprintk("%s Bad first_stripe_index %u\n",
__func__, fl->first_stripe_index);
@@ -598,6 +600,13 @@ filelayout_check_deviceid(struct pnfs_la
goto out_put;
}
status = 0;
+
+ /*
+ * Atomic compare and xchange to ensure we don't scribble
+ * over a non-NULL pointer.
+ */
+ if (cmpxchg(&fl->dsaddr, NULL, dsaddr) != NULL)
+ goto out_put;
out:
return status;
out_put: